A. Field of the Invention
The present invention relates to an apparatus and method for controlling picture inversion of a liquid crystal display (hereinafter referred to as "LCD").
B. Description of the Prior Art
A conventional LCD includes, as shown in FIG. 1, a video processor 1 for processing an externally-supplied signal to provide a mixed video signal, and a signal processor 2 for receiving the mixed video signal from video processor 1 to provide a composite sync signal with a vertical sync signal and a horizontal sync signal and a signal without the sync signals. In addition, a sync signal generator 3 receives the composite sync signal from signal processor 2 and a control signal from a controller 5 to provide another new sync signal by means of a sync signal supplied from an internal sync signal generating device, and controller 5 provides control signals to sync signal generator 3 and an LCD part 6 responsive to a key signal supplied from a key input part 4. Also, LCD part 6 receives R, G, B video signal from signal processor 2 and the sync signal from sync signal generator 3 to display an image in accordance with the control signal from controller 5.
In the conventional LCD formed as described above, as shown in FIG. 1, once the externally-supplied signal is received into video processor 1 to provide the mixed video signal, signal processor 2 receives the mixed video signal from video processor 1 to separate the composite sync signal having the vertical sync signal and horizontal sync signal and supply it to sync signal generator 3 while supplying the other composite sync signal to LCD part 6.
At this time, sync signal generator 3 receives the composite sync signal supplied from signal processor 2 to supply the new sync signal to signal processor 2 and LCD part 6 in accordance with the control signal from controller 5. Simultaneously, the sync signal generator 3 supplies the control signal to LCD part 6.
When the new sync signal supplied from sync signal generator 3 is received into signal processor 2, signal processor 2 synchronizes the R, G, B signal with the new sync signal from sync signal generator 3 to supply the resultant signal to LCD part 6.
After the R, G, B signal from signal processor 2 and various control signals from sync signal generator 3 are supplied to LCD part 6 in the foregoing manner, the normal image is displayed on LCD part 6 in accordance with the control signal from controller 5.
If a picture inversion signal is provided from key input part 4 while the normal image is displayed on LCD part 6, controller 5 receives the picture inversion signal from key input part 4 to supply it to sync signal generator 3. Following this, sync signal generator 3 changes the control signal to correspond to the picture inversion in accordance with the received picture inversion signal to supply the changed signal to LCD part 6. By this operation, LCD part 6 inverts the currently-displayed image in accordance with the picture inversion control signal supplied from controller 5.
FIG. 2 shows timing charts of respective signals in the conventional LCD. Referring to FIG. 2, (a) shows vertical sync signals; (b) horizontal sync signals; (c) picture inversion signal; and (d) picture inversion control signal.
In other words, if the picture inversion signal (c), as shown in FIG. 2, is provided from key input part 4 when the mixed video signal supplied from video processor 1 includes the vertical sync signal (a) and horizontal sync signal (b), controller 5 receives the picture inversion signal (c) during a prescribed time period .DELTA.t1 and provides the picture inversion control signal (d) within a prescribed time period .DELTA.t2.
FIG. 3 illustrates pixels in the vertical axis and horizontal sync signals of the LCD. In case of the NTSC, the image is displayed such that the actually-displayed video signals on LCD part 6 are the 15th horizontal to the 248th horizontal sync signal when the vertical axis pixels number approximately 234. The image is not displayed on LCD part 6 at the horizontal sync signals in the sections H1 to H14 and H248 to H263.
The picture inversion is attained when the picture inversion signal is received into the displayed image in case that the time (obtained by .DELTA.t1+.DELTA.t2 from the vertical sync signal) taken for providing the picture inversion control signal from controller 5 in response to the picture inversion signal from key input part 4 exists within the section from H15 to H248. However, an arbitrary signal, one other than the original video signal, is displayed on the LCD part during the time (of approximately 2H to 5H) for executing the picture inversion. Thus, the conventional LCD heretofore has a problem of producing a severe noise on the LCD part.